The present invention relates generally to radiocommunication systems and methods for signaling in radiocommunication systems and, more particularly, to systems and methods for communicating emergency messages over non-voice communication channels in radiocommunication systems.
GSM (Global System for Mobile Communications) describes a European standard for radiocommunication and the corresponding Public Land Mobile Network (PLMN) which is intended to provide uniformity so that users can access radiocommunication systems throughout Europe with minimal equipment compatibility problems. GSM includes many services for subscribers, including a message function service called the Short Message Service (SMS) which provides for the transmission of text messages having up to 160 alphanumeric characters to be sent to or from a subscriber at his or her mobile unit.
When an SMS message is delivered from a service center to a mobile unit, regardless of how it originates, such a message is conventionally referred to as a xe2x80x9cmobile terminated short messagexe2x80x9d (MTSM). If an SMS message originates at a mobile unit, the signal to the service center requesting forwarding of the SMS message is conventionally referred to as a xe2x80x9cmobile originated short messagexe2x80x9d (MOSM). It is the MOSM which is the focus of the present invention.
In a GSM-based cellular or satellite communication process, such as the Asia Cellular Satellite system (ACeS), a procedure referred to as xe2x80x9cconnection establishmentxe2x80x9d identifies the type of call (e.g., an emergency call) initiated by or terminated at a mobile station. One skilled in the art will appreciate that GSM-based systems include, but are not limited to, GSM-based systems operating in the 900 MHz, 1800 MHz or 1900 MHz range.
Connection establishment involves the initial handshaking and exchange of control information between a mobile station and a GSM-based network, which occurs before a connection is established. This procedure gives GSM-based networks the ability to determine the eligibility of a mobile phone user to place a particular call (e.g., whether to grant or deny to certain users connection of certain calls based upon the user""s subscription type). In the case of emergency calls, the establishment procedure is used by networks to grant open access to all users, regardless of subscription restrictions or other conditions that would normally block access for other types of calls.
An example of a call restriction placed on a GSM mobile phone user is one that may apply when the user""s subscription belongs to a different network than the network which supports radiocommunication service in the area in which the user""s equipment is currently located. For example, the two networks may not have a roaming agreement there between. Such a user may normally be denied access. As a result, the user would be unable to place normal phone calls or use other GSM services, such as the short messaging service (SMS), which require such access. In this instance, only emergency voice calling (i.e., calls to emergency numbers) may be available to the user. Such conventional emergency call handling procedures are set forth in xe2x80x9cEuropean Digital Cellular Telecommunications System (Phase 2); Man-Machine Interface (MMI) of the Mobile Station (MS),xe2x80x9d GSM 02.30, Version 4.10.0, October 1993; xe2x80x9cDigital Cellular Telecommunications Systems (Phase 2); and Mobile Radio Interface Layer 3 Specification,xe2x80x9d GSM 04.08, Version 4.9.0, July 1994, all of which are hereby expressly incorporated by reference.
There may be emergency situations in which a user would like or need to send a character or data message instead of placing an emergency voice call. For example, if a person was having a heart attack and was unable to speak, the transmission of a data message could possibly be the only way in which the person could summon emergency assistance. Such an emergency message could include, for example, the user""s geographical location. In current GSM-based systems, however, the user would have to place a normal (non-emergency) call in order to send such a data message. When a user is restricted from placing normal calls, emergency data messages could not be sent.
Because GSM-based standards define emergency calls for voice only, only voice messages can be transmitted via a mobile station to an emergency operator. FIG. 1 illustrates a conventional emergency calling procedure for a GSM-based system. When a call is initiated from a mobile station, it transmits a CHANNEL REQUEST message to the cellular or satellite network (step 110). The CHANNEL REQUEST message contains an information element called the xe2x80x9cEstablishment Cause.xe2x80x9d The Establishment Cause, as the name suggests, provides the network with the type of call being established. Typical values for the Establishment Cause include: Answer to paging, Call re-establishment, Emergency call, Originating data call, Originating speech call, Location updating, and procedures that complete on the Stand Alone Dedicated Control Channel (SDCCH). The SDCCH cause indicates Short Message Service is desired. For emergency calls, the Establishment Cause is set to Emergency Call.
In response to the CHANNEL REQUEST, the network sends an IMMEDIATE ASSIGNMENT message to the mobile station, directing it to a dedicated control channel on which call setup can proceed (step 120) as follows.
After accepting the IMMEDIATE ASSIGNMENT message, the mobile station requests a service from the network by sending a service request message (step 130). In FIG. 1, a CM SERVICE REQUEST message is sent. The CM SERVICE REQUEST message contains a CM Service Type information element, which indicates the type of service desired. The CM Service Type can assume one of the following values: MS Originating Call Establishment, Emergency Call Establishment, Short Message Service, and Supplementary Service Activation. For an emergency call, the CM Service Type is set to Emergency Call Establishment.
When the ESTABLISHMENT CAUSE indicates that the mobile station requests an emergency call (i.e., the CM Service Type is set to Emergency Call Establishment), only an emergency voice call is permitted. Emergency calls in conventional GSM-based systems are specified only for mobile stations that support telephony. Hence, there is no way for a user to request emergency assistance from an emergency operator other than through voice transmissions.
The present invention overcomes the above-identified deficiencies in the art by providing a method for communicating emergency messages using non-voice connections. According to exemplary embodiments of the present invention, an emergency short message service is added to existing digital wireless specifications, such as GSM-based systems. This service allows users to place an emergency call with the specific purpose of sending an emergency data message using Short Message Service (SMS). Such data messages might include the caller""s geographical position, electronic mail messages, or possibly, diagnostic information. The emergency data messaging service of the present invention will be given the same access conditions as voice emergency calls in a cellular or satellite system.